Project Summary/Abstract The severity of T1D complications warrants an urgent need to improve glycemic control since 22% and 17% of children and adolescents with T1D, respectively, have suboptimal A1C >9.5%. Moreover, the T1D Exchange recently showed that an average A1C of 9% in 13-17 year olds is not much lower than the A1C average of 9.5% seen in the same age group at the beginning of the DCCT over 30 years ago. In fact, youth ages 2-17 years have an average A1C of 8.6%. In addition, there is an alarmingly high rate of pediatric DKA in the United States, with 7% of youth <18 years of age hospitalized for DKA. NIDDK recognizes that diabetic ketoacidosis (DKA), a serious acute complication, in youth must be addressed and strategies to reduce it developed, including significantly reducing time spent in hyperglycemia. Suboptimal adherence to critical T1D management behaviors (e.g., blood glucose monitoring, insulin dosing), either alone or in combination with psychosocial stressors, may lead to suboptimal glycemic control. Indeed, individuals with T1D and mental health comorbidities are 2x as likely to be in suboptimal glycemic control, yet 30% of T1D care teams do not have access to onsite mental health services. Moreover, mental health comorbidities are associated with worsening long-term complications. One possible pathway to improving glycemic control is to increase access via home telehealth This study is novel as it will use home telehealth intervention to address suboptimal T1D management and glycemic control by integrating medical and behavioral health (i.e., psychological) interventions to reduce negative and costly physical health outcomes in high-risk youth with T1D. The primary objective of this study is to address the critical need of providing intervention to high-risk (A1C=9-12%) youth with T1D. If achieved, T1D care practices will change by providing high-risk youth with T1D and their parents medical and behavioral health support via home telehealth intervention, which has the potential to significantly change access to T1D care, decrease time spent in hyperglycemia, reduce the frequency of hospital admissions, and improve glycemic control. In addition, use of Multiphase Optimization Strategy (MOST), a highly efficient experimental strategy to determine effective intervention components, should be generalizable to all individuals with T1D, leading to cost-effective, home telehealth intervention programs. Innovative aspects include: 1) assessment of physical and behavioral health characteristics associated with high-risk status; 2) delivery of home telehealth that incorporates: 2a) medical and behavioral health care delivered with the endocrinologist and behavioral health specialist working together with high-risk youth; 2b) personalized intervention to improve T1D adherence and T1D clinical health outcomes; 2c) personalized intervention to improve mental health comorbidities and T1D clinical health outcomes; and 3) an underused methodological approach for optimizing intervention components to be delivered at point of care.